De novo-synthese von verzweigten dl-pseudoglycalen

Z-1-Methoxybutenyne $\text{1}$ was used for the synthesis of Z,E-1-methoxybutadiene derivatives $\text{2}$–$\text{7}$. Hetero-Diels-Alder reactions with diethyl mesoxalate $\text{8}$ led to the C-4 branched pseudoglycals $\text{9}$–$\text{14}$, $\text{16}$ and to the glycal $\text{15}$, respectively. The bicyclic lactone $\text{17}$ was obtained by dealkoxycarbonylation of $\text{16}$.